In laboratory tests, 3% STPP ‘(sodium tri poly phosphate, the mineral phosphate salt widely used last century in detergents) and pomegranate rind extract were tested as a “green” PIN flame retardant treatment for cotton (150 g/mm2 woven fabric). The extract was obtained by high temperature boiling in water of chopped waste pomegranate rinds. The cotton was soaked in STPP and then extract for 30 minutes each at 90°C, then dried. The pomegranate extract includes nitrogen-containing alkaloids, which are considered to contribute to flame retardancy, and metal ions which react with the negative STPP ions. The combined treatment achieved self-extinguishing in the cotton, but caused brown discoloration, and was not wash durable. Wash durability was however obtained by treating with citric acid and a phosphorus-based catalyst.
“Sodium tri-polyphosphate in combination with pomegranate rind extracts as a novel fire-retardant composition for cellulosic polymer”, S. Basak & S. Wazed Ali, Journal of Thermal Analysis and Calorimetry https://doi.org/10.1007/s10973-019-08034-w